The present invention relates to disposable, medical electrodes. Medical electrodes are adhered to a patient's body either to collect or introduce electricity at specific points. Those electrodes collecting electricity are categorized as either monitoring or diagnostic electrodes. The so-called "TENS electrodes" are categorized among those electrodes which introduce electricity into the patient's body. The present invention is particularly useful for monitoring/diagnosing a patient's physiological potentials, as in an electrocardiogram examination. However, it can also be adapted for use as a TENS electrode.
The principal functional components of the typical prior art monitoring/diagnostic electrode include a conductive layer, a conductive contact to which leads from a monitoring/diagnostic apparatus can be connected, and a support member upon which the two aforementioned components are mounted. Generally, the support or carrier has a conductive-adhesive backing so that the electrode can be securely fastened to the patient. The conductive layer and contact are typically a conductive hydrogel and a metal snap fastener, respectively. In some of the prior art, U.S. Pat. No. 3,977,392 being exemplary, the conductive hydrogel and metal snap fastener are spaced apart on the carrier medium. A strip of conductive material, such as silver foil, acts as a bridge between the two components to complete the electrical connection. Such a configuration is known as an offset electrode. Offset electrodes are known in the prior art to be advantageous over electrodes which intimately connect the snap fastener to the hydrogel, since the latter configuration speeds up corrosion of the snap fastener. This corrosion jeopardizes the accuracy of the electrode, making it all but useless.
Under either the offset or direct-connect configurations, the prior art discloses a variety of methods for attaching all the necessary conductive components to the carrier or support. U.S. Pat. No. 3,977,392 discloses essentially disc-shaped conductive hydrogel, resting in an opening in the carrier of approximately the same size as the hydrogel. The conductive layer of silver foil, being slightly less wide than the hydrogel disc, is placed on top of the carrier, conductively connecting the hydrogel and a metallic snap-fastener stud. A top layer, having an adhesive underside, is placed on the carrier medium, trapping the conductive components underneath. The adhesive underside of this top layer adheres to those portions of the hydrogel not covered by the conductive foil. Thus, the hydrogel is maintained in its opening in the carrier medium. However, in practice this method is not always effective. Being "sticky" by nature, the hydrogel will often adhere to the release paper or other protective backing, overcoming the adhesive effects of the aforementioned top layer. This has the effect of pulling the hydrogel from the carrier medium, such that the user is forced to tamper with the gel to get it back in place or abandon the electrode and try again.
U.S. Pat. No. 4,559,950 discloses an alternative arrangement where a silver-ink coated conductive layer directly contacts a patient's skin. The conductive hydrogel is maintained in a reservoir on top of the conductive layer. When pressure is applied to the reservoir, the hydrogel moves through a narrow slot in the conductive layer to form a more sensitive bridge between the patient's skin and the conductive layer. The ring-shaped reservoir of '950 has an adhesive underside, by which it is attached to the considerably smaller conductive layer, leaving additional areas of adhesive to attach the entire electrode to a patient's skin.
Still other medical electrodes either employ no hydrogel per se or use an adhesive conductive gel which is simply "stuck" to the surface of the conductive bridge in an offset-type electrode. For those monitoring/diagnostic electrodes which employ no conductive hydrogel, the accuracy of their electrical signal transmission can be seriously jeopardized where a patient's skin is covered with a substantial amount of hair fibers. Neither does merely attaching, as in the alternative configuration, an adhesive hydrogel to the surface of the conductive bridge insure that the gel will adhere to the electrode where the unit is misplaced on a patient's body and must be removed and repositioned.